The objective of this proposal is to initiate a program of study of sequencing behavior using pigeons and squirrel monkeys as subjects. The subjects will be tested using a discrete trials procedure where at the beginning of a trial, several color stimuli are simultaneously presented on side-by-side operanda with the location of a given color varied in a random fashion between trials. The behaviors required are the selection of (response to) the color stimuli in a predetermined sequence with the required sequence remaining constant over sessions. Completion of the required sequence will result in food delivery and an intertrial interval. Various consequences may be scheduled for correct and incorrect responses (selections) within the sequence. A second sequence will be introduced after the first sequence is acquired. A different discriminative stimulus will be associated with each sequence (i.e., a conditional discrimination for sequences). That is, in the presence of stimulus A, the subject will be required to select the color stimulis in a different order. Eventually, a number of variants of stimulus control of sequences will be investigated. Sequencing behavior is more complex than most preparations used for the study of stimulus control of animal behavior and has greater similarity to behavior in the natural environment and in complex experimental tasks where the more meaningful behavioral unit for analysis is typically a sequence of related behaviors, not a single operant. The proposed research is an attempt to apply the concept of stimulus control to extended sequences of behavior so to better understand such sequences as well as more complicated behavioral tasks where sequencing behavior is one part of the overall behavioral requirement.